1. Field of the Invention
The present invention relates to power systems, and more specifically, to a power-assisting system of a mobility vehicle.
2. Description of the Related Art
Common personal mobility vehicles, such as bicycles, wheelchairs, baby buggies, trolleys and so on, are moved by human-power with hands or legs. It takes considerable energy and physical strength when the mobility vehicle is loaded heavily or moves uphill, which causes muscle fatigue. While, when the mobility vehicle moves downhill, the mechanical kinetic energy is converted to unrecyclable heat energy due to the use of a mechanical brake. Therefore, the mobility vehicle is often inefficient and energy-wasting in such applications.
Accordingly, power-assisted devices such as power-assisted bicycles or power-assisted wheelchairs are developed. In such devices, the driving wheel is replaced with an electric motor, and the pedaling or hand-propelling is detected by a sensor. The sensed signal is amplified as a command to a power amplifier, and finally a motor force is generated to assist the movement, especially when moving uphill. Moreover, the power-assisted mobility vehicle can adjust the magnification of the motor force to a desirable value through a connection with a micro-computer. A switch or an electric throttle can be incorporated to switch the mode of operation among the manual mode, the power-assist mode and the full electric mode, so as to save the electrical power or human labor.
However, as far as the conventional power-assisted bicycles and power-assisted wheelchairs are concerned, a force/torque sensor is often required to sense the human power; such sensors are expensive and may not convert the force instantaneously due to the limited bandwidth. Moreover, the calibration of the sensors is laborious which would cost engineering resources. Finally in order to mechanically accommodate the force/torque sensor, the mechanism of mobility vehicle has to be modified significantly.
Some of the conventional mobility vehicles, including the power-assisted bicycles or the power-assisted wheelchairs, may instead utilize a single-axial accelerometer as a level gauge to detect the inclination angle when the device is on a slope. In such a case, the accelerometer outputs a signal to the electric motor to generate an assisting force to cancel out gravitational force. By doing so, the required human power to move the mobility vehicle on the ramp is reduced.
However, when the accelerometer detects the inclination angle based on the projection of the gravitational force along the ramp direction, the inclination angle will be inaccurate if the mobility vehicle is operated in an accelerating or decelerating state, or is operated on a bumpy road, because the acceleration of the mobile device is also picked up by the accelerometer. In practice, it is typically assumed that the frequency of the acceleration is much higher than the frequency of inclination angle change, so the inclination angle can be obtained separately by filtering the accelerometer signal via a low-pass filter. However, filtering causes a time lag on the inclination angle detection which in turn causes a delay in the acquisition of the inclination angle. As a result, there will be a lag in the power assisting performance when the mobility vehicle first entering a ramp.
Moreover, although it has been proposed that by combining the acceleration output of a single-axial accelerometer and the absolute angular velocity of a gyroscope via signal fusion, one can reduce the delay in the inclination angle sensing, such a method still cannot completely eliminate the influence of acceleration/deceleration of the mobility vehicle on the inclination angle measurement. Also, when the mobility vehicle moves under large slope variations or performs multi-degree-of-freedom movement (e.g., when a bicycle or a wheelchair moves with a lateral tilt or a turning), such a signal fusion method could generate an erroneous output due to the nonlinearity in the system dynamics as well as the dynamic coupling effect.
Therefore, there is a need in the industry to overcome the problems of the conventional power-assisting techniques in mobility vehicles.